Cyclic water hammer method



1968 J. KARPOVICH CYCLIC WATERv HAMMER METHOD 2 Sheets-Sheet 1 FiledJune 27, 1966 INVENTOR. Ja/nv kar oaw'c/i United States Patent Oflice3,409,470 CYCLIC WATER HAMMER METHOD John Karpovich, Caro, Mich.,assignor to The Dow Chemical Company, Midland, Mich., a corporation ofDelaware Continuation-impart of application Ser. No. 195,660, May 11,1962. This application June 27, 1966, Ser. No. 563,626

4 Claims. (Cl. 134-1) This application is a continuation-in-part of mycopending application Ser. No. 195,660, filed May 11, 1962, for CyclicWater Hammer Apparatus, now abandoned.

This invention relates to a method for generating socalled cavities in aliquid system in an enclosed vessel to facilitate mixing, cleaning orthe like within the said vessel.

The use of ultrasonic means for generating cavities in a liquid systemand using the cavities in a number of operations such as cleaning andmixing, for example, are well known.

However, the generation of cavities by ultrasonic means usually involvesthe use of an electronic oscillator and an associated transducer, andsuch apparatus is by its nature somewhat complicated and expensive.

Accordingly, a principal object of this invention is to provide animproved method for cleaning enclosed vessels.

Another object of this invention is to provide an improved, simpler andmore economical method for removing adherent materials from surface ofenclosed vessels.

A further object of this invention is to provide an improved method ofcleaning surfaces of elements contacted by a liquid system in anenclosed vessel.

Still .another object of this invention is an improved method forcleaning surfaces of heat exchanger apparatus.

In accordance with one embodiment of this invention there is providedapparatus for generating cavities in a liquid medium, usually in acyclically recurring manner, comprising a quick opening and closingvalve having an input flow bore, a pair of output florw bores, thisvalve being adapted to alternately bl ock flow through each of theoutput flow b'ores. The input to the valve is coupled to a line havingliquid therein which is pumped through the valve while at least one ofthe output flow bore-s is coupled to the interior of a vessel to becleaned. As liquid base material is pumped through the valve, the rapidopening and closing of the valve output bore results in the liquidbeyond the shutoff point being placed in tension, generating cavities inthe liquid. At the same time, the vessel surface to be cleaned is heatedto a temperature at which surface boiling occurs under the conditionspresent when the liquid base material is under tension.

With the collapse of the thus generated cavities due to the stoppage offlow of the liquid base material beyond the valve, surface boilingoccurs .at and along the heated surface or surfaces of the vessel. Thecombination of the cavitation plus surface boiling results in theloosening and removal of adherent materials from the surface beingcleaned.

The surface being cleaned may be .a tube, of a heat exchanger, forexample, or any inner surface of an enclosed, pressurizable vessel.

The invention, as well as additional objects and advantages thereof,will best be understood when the following detailed description is readin connection with the accompanying drawings, in which:

FIG. 1 is a schematic view of cyclic water hammer apparatus inaccordance with this invention;

FIG. 2 is a side elevational view, partly broken away 3,409,470 PatentedNov. 5, 1968 and in section, of one form of flutter valve which isadapted for use in this invention;

FIG. 3 is a schematic illustration of a multiple valved cyclic waterhammer apparatus in accordance with this invention; and

FIG. 4 is a schematic view of a heat exchanger apparatus made inaccordance with this invention.

Referring to the drawing, and particularly to FIG. 1, there is shownapparatus for generating cavities in a liquid system comprising a pump10, usually of the centrifugal or continuous flow type, which is coupledto a flow loop, indicated generally by the numeral 12, which along asubstantial part of its length is divided by .a partition 14 into twoflow channels 16, 18. A flutter valve 20, pivotally coupled to the end22 of the partition 14 which faces the oncoming flow from the pump 10,is adapted to seat and close, in turn, each of the flow channels 16, 18,for example.

A pressure release reservoir or compliance element 24 is coupled to theflow loop 12 ahead of the pump 10 in the direct-ion of liquid flow fromthe pump.

In operation, the flow loop and part of the pressure release reservoiror vessel 24 is filled with a pumpable liquid base medium such as oiland water, for example. The pump is then started, pumping the liquidbase medium in the direction of the arrow 26 towards the end 22 of thepartition 14. The flutter valve 20 is easily swung to close one or theother of the channels 16, 18. Assuming, for example, that the fluttervalve suddenly closes the channel 18, a Water hammer occurs and theliquid base medium beyond the closed valve is placed in tension untilthe tensile strength of the liquid is overcome, causing the liquid tofracture and produce cavities. The produced cavities are unstable,bearing under pressure from the surrounding liquid, and will collapsesuddenly, resulting in the generation of shock waves inn the liquid. Theformation and collapse of such cavities is often referred to ascavitation.

The function of the pressure release vessel is to act as a de-surger toisolate the pump from the flutter valve and to accommodate excess liquidwhen cavities are formed in the closed system. After the cavities areformed, the liquid in the flow channel which is closed off at one end bythe flutter valve 20 changes its direction of flow as the cavitiescollapse and hammer back, opening the valve 20 and causing it to closethe flow channel 16. This cyclic closure behavior of the flutter valvecontinues in a repetitive manner, resulting in a cyclic water hammer andshock wave generation.

The arrangement of FIG. 1 can be regarded as a mechanical oscillator.The apparatus shown in FIG. 1 is used to make an oil and water emulsionor may be used, for example, in the mixing or treating of liquids whichmay or may not be subjected to external influences while in theapparatus. Examples of external influences are heat and radiation.

Referring now to FIG. 3, it may be seen that the apparatus of thisinvention is useful in systems where the liquid base medium passesthrough the device only a single time and is not recirculated as withthe apparatus shown in FIG. 1.

In the apparatus shown in FIG. 3, the liquid base medium is pumped bymeans of a pump 28 from a first vessel 30 to a second vessel 32. A flowline, indicated generally by the numeral 34, is coupled through the pump28 and extends from the vessel 30 into the vessel 32. The line 34 isdivided into two separate flow channels at a plurality of places alongits length by means of partitions 36, 38, 40, for example.

A flutter valve 42, similar to the valve 20 in FIG. 1, is pivotallymounted at the end of partition 36 where the liquid base flow mediumenters the flow channels 43,

. 3 a 44 and is adapted to close either of the channels 43, 44,depending on the conditions of operation existing in the apparatus.

Similarly, the valves 46, 48 are pivotally mounted at the fluid entryend of each of the partitions 38, 40 to alternately close the flow paths50, 52 and 54, 56.

In operation, the apparatus acts similarly to the apparatus shown inFIG. 1, except that each separate flutter valve and its associated flowpath acts to sequentially generate cavities in the respective flow path,as does the valve and flow paths 16, 18, to provide a much largerpopulation of cavities in the liquid flowing from the vessel to thevessel 32 than would occur if only a single valve and flow patharrangement were to be used.

Referring now to FIG. 2, there is shown a flutter valve assembly,indicated generally by the numeral having a T shaped body section 62which has a liquid input line 64 and liquidoutput lines 66, 68 whichcommunicate with each other. The transverse diameter of the input line64 is preferably, but not necessarily, larger than the transversediameter of each of the output lines 66, 68. The inner or body ends 70,72 of the output lines 66, 68 are each shaped to form a seat for a ballvalve 74 which is disposed within the body 62 of the valve 60. The wallpart 76 of the body 62 lying between the valve seat ends 70, 72 iscurved slightly so that when no liquid medium is being pumped throughthe device the ball valve 74 tends to lie away from both of the valveseats 70, 72 and slightly off center with respect to the path of fluidflow from the input line to the output lines.

In operation, the slightly off center at rest position of the ball valve74 assures that when liquid is pumped or passed through the inlet line64 and out the outlet lines 66, 68 that the ball will be carried alongby liquid and seat against one of the seats 70, 72. The sudden seatingof the ball causes a water hammer to occur in the Output line ahead ofthe seated ball and in that output line the liquid goes into tension andforms cavities. As the cavities collapse, the surge of force resultingtherefrom forces the valve off its seat and towards the other valveseat. The valve is then carried towards the other seat by the flow ofliquid after it passes the midpoint between the two valve seats. Again,the seating of the ball valve 74 causes a water hammer, the productionof cavities in the liquid in the closed output line, and the subsequentunseating of the ball valve -by the collapse of the cavities as before.

The mechanical oscillator arrangement shown in FIG. 2 may be used as arethe flutter valves 20, 42, 46, or 48 in FIGS. 1 and 3 where the larger,full diameter part of the flow line 12 or 34 is the input line 64 to thedevice 60 and the flow channels 16-18, 4344, 50-52, and 54-56 are theoutput lines 66, 68 of the device.

Another embodiment of this invention is shown in FIG. 4.

In the apparatus of FIG. 4, a liquid is driven through the line 80 bythe pump 82 (or other driving means not shown). A compliance element 84,illustrated as a surge tank, for example, is coupled to the line 80between the pump 82 and a flutter valve 20 illustrated in FIG. 1. Thevalve assembly 86 comprises the flutter element (or valve) 88 and valveseats 90, 92 which communicate with the input end of the hollow tubes94, 96. Alternatively, other types of quick opening and closing valvesmay be used across the tubes 94, 96 to place the pressurized liquid inthe tubes in tension and produce a water hammer.

The tubes 94, 96 terminate at their output end in a common header 98 andare then coupled to some utilization means, not shown. The tubes 94, 96are surrounded by and enclosed in an enclosed vessel such as a heatexchanger jacket 100 having an inlet 102 and an outlet 104 by means ofwhich a heat exchanger fluid, such as steam, for example, is circulatedthrough the jacket 100' and around the tubes 94, 96.

4 As liquid, e.g., water, is pumped through the apparatus, the valveelement 88 of the flutter valve assembly suddenly closes against one ofthe valve seats or 92, placing the liquid behind the valve (i.e., in thedirection in which liquid normally flows) in tension and causing theproduction of cavities in the liquid. As stated previously, theformation and collapse of such cavities is often referred to ascavitation.

On collapse of the so-produced cavities, the liquid in the flow channelor tube whose end has been closed by the flutter valve 88 hammers 'backand knocks the flutter valve across so that the end of the other channel(94 or 96) is closed. Cavities then form in the newly closed tube,collapse, flip the flutter valve to close the other tube, and therepetitive process continues.

The heat exchange fluid applied to the heat exchange jacket may beeither hotter or cooler than the liquid in the line 80, but should be ata temperature wherein boiling of liquid at the heated surface occurswhen the liquid is placed under tension and cavitation occurs.

Further, if the temperature of the tube walls (or of any surface to becleaned in accordance with this invention) is, under treatingconditions, above the boiling temperature of the liquid base flowmaterial, the flow rate of the liquid base material is maintained atsuch a rate that the liquid base flow material does not reach boilingtemperature as it passes through or along the surface to be cleanedexcept when the liquid base material is under tension.

When the liquid pumped or flowing under pressure through the tubes 94,96 of the heat exchanger is of a type which tends to form a coating ordeposit, such as water deposited scale, on the walls of the tube duringusage of the device, it has been found that the heat transfercharacteristics of a heat exchanger in which periodical placing the flowliquid under tension momentarily was done are much better than foridentical tubes in a heat exchanger wherein no cavity generating meanswas incorporated. Measurements of these characteristics were made atintervals over an extended time period.

Thus, while this invention has particular merit as a method of cleaningadherent materials from surfaces of an enclosed element or vessel, theperiodic placing of the liquid flow material under tension and theconsequent momentary production of surface boiling constitutes a methodof preventing or greatly slowing of the buildup of adherent materials onsuch surfaces (assuming surface temperatures during normal operation ofthe element or vessel are sufficient to cause surface boiling).

Usually the flutter valve assembly (or its equivalent) is placed closeto (about a foot away from) the input end of the tubes to be cleaned (orkept clean). The length of the tubes 94, 96 is, for best results manytimes their diameter.

It is also practical to use one flutter valve assembly to operate twoheat exchangers.

If the tubes of each exchanger are coupled to a common header, the tubes94, 96 each may be coupled to a separate header of a heat exchanger. Inevent the fluid (liquid) in the heat exchanger jacket of each exchangeris to be cavitated to produce a cleaning or scale (deposit) removingaction, the connections to the tubes 94, 96 could instead be made to theinput (102 in the illustration) of the heat exchanger jackets. With sucha setup, the outer surfaces of the heat exchanger tubes and the wallsurfaces of the heat exchangers would be cleaned.

If the liquid contacting the part of the exchanger which is to becleaned is inexpensive, such as water, for example, it is, of course,practical to use only the tube connected to one valve of the fluttervalve assembly in the cleaning operation while the other tube or leg ofthe device is a line through which the liquid is conducted to waste orto a tank for re-use. The leg or line which is not coupled to the heatexchanger should preferably be as long or longer than the other linewhich is coupled to the heat exchanger in order to avoid wasting undulylarge amounts of liquid.

Because the method of this invention is equally applicable to thecleaning of enclosed pressurizable vessels in general, the outer wallsof the tubes 94, 96, as well as the walls of the heat exchanger jacket,may be cleaned (or kept clean) by coupling one of the output lines fromthe valve 88 to the input 102 of the heat exchanger jacket, for example.In such a setup, the output 104 of the heat exchanger jacket may becoupled to a return line to a liquid base material source, or to waste.

The cyclic closing of the flutter valve if such a 'valve is used, is afunction of the characteristics of the system in which it works, butcyclic rates of from 1 cycle per minute to somewhat over 400 cycles perminute have been used.

Excellent cleaning of (or the prevention of a buildup of a depositon)heat exchanger tubes and surface parts of other enclosedpressurizable vessels has been accomplished when the flutter valveassembly is in operation only one-half hour in a 24 hour period ofoperation at a flutter valve cyclic opening and closing rate of about1.5 cycles per second.

Although not shown in the drawing, the test setup used had valving meanswhereby the flutter valve assembly could be bypassed during the time thevalve was not in operation.

The pressure of the liquid in the line 80 may vary from 5 p.s.i. to4,000 p.s.i., for example, but a pressure of 65 pounds per square inchon the liquid base flow material (which was readily available) hasoperated the heat exchanger device of FIG. 4 very well during tests.

While a flutter valve has been described in connection with theoperation of the invention, the ball valve of FIG. 2 or other type ofquick opening and closing, double or single acting mechanical valves(s),of course, may be used as a substitute. The ball valve may be made ofmetal, a solid state plastic, wood, or any suitable material.

While pressure limits approaching one pound/sq. inch to several hundredpounds/sq. inch have been tested, the upper pressure limit is, inpractice, apparently limited only by the ability of the apparatus towithstand the pressure.

The heating of the surface to be cleaned may be accomplished by steam,as mentioned, or by flame, resistance heating, induction heating or anysuitable means.

What is claimed is:

1. A method of removing material adhering to a surface part of anenclosed vessel which is adapted to be pressurized, said vessel havingspaced apart inlet and outlet means for passing liquid base flowmaterial over said surface part, comprising flowing liquid which isunder pressure along said surface part, heating said surface part to becleaned to above the boiling temperature of said flowing liquid undertensile stress conditions, and then suddenly interrupting the flow ofliquid at said inlet means thus placing said liquid under tensionwhereby boiling occurs at said surface part.

2. A method in accordance with claim 1, wherein said liquid base flowmaterial is flowed past said surface part at a volumetric rate such thatgeneral boiling does not occur while said material is flowing.

3. A method in accordance with claim 1, wherein the flow of said flowingliquid base material is interrupted at a rate of between 5 cycles/minuteand 250 cycles/minute.

4. A method of removing material adhering to a wall surface of a heatexchanger having tubes which have inner and outer walls, and which hasspaced apart inlet and outlet means for passing liquids over said wallsurface, comprising flowing liquid which is under pressure along saidwall surface between said inlet and outlet means, heating said surfaceto be cleaned to above the boiling temperature of said flowing liquidunder tensile stress conditions, and then suddenly interrupting the flowof liquid at said inlet means thus placing said liquid under tensionwhereby boiling occurs at said wall surfaces.

References Cited UNITED STATES PATENTS 1,628,530 5/1927 Burnett 134221,840,834 l/1932 Davis -84 2,089,317 8/1937 Wilder 134--22 2,123,4347/1938 Paulson et al 13422 2,514,797 7/1950 Robinson 165-84 2,664,27412/1953 Worn et a1. 16584 MORRIS O. WOLK, Primary Examiner.

I. T. ZATARGA, Assistant Examiner.

1. A METHOD OF REMOVING MATERIAL ADHERING TO A SURFACE PART OF ANENCLOSED VESSEL WHICH IS ADAPTED TO BE PRESSURIZED, SAID VESSEL HAVINGSPACED APART INLET AND OUTLET MEANS FOR PASSING LIQUID BASE FLOWMATERIAL OVER SAID SURFACE PART, COMPRISING FLOWING LIQUID WHICH ISUNDER PRESSURE ALONG SAID SURFACE PART, HEATING SAID SURFACE PART TO BECLEANED TO ABOVE THE BOILING TEMPERATURE OF SAID FLOWING LIQUID UNDERTENSILE STRESS CONDITIONS, AND THEN SUDDENLY INTERRUPTING THE FLOW OFLIQUID AT SAID INLET MEANS THUS PLACING SAID LIQUID UNDER TENSIONWHEREBY BOILING OCCURS AT SAID SURFACE PART.